a. Field of the Invention
The instant invention is directed to therapeutic ultrasound systems, such as surgical HIFU ablators, comprising acoustic energy waveguides and acoustic energy-guiding applicators for imparting the acoustic ablative energy to, into or upon target tissues. The instant invention allows for inexpensive if not disposable energy applicators which connect to a nondisposable energy waveguide which in turn connects to an energy providing console.
b. Background Art
Catheters have been in use for medical procedures for many years. Catheters may be used for medical procedures to examine, diagnose, and treat while positioned at a specific location within the body that is otherwise inaccessible without more invasive procedures. During these procedures a catheter is inserted into a vessel located near the surface of a human body and is guided to a specific location within the body for examination, diagnosis, and treatment. For example, one procedure often referred to as “catheter ablation” uses a catheter to apply localized radiofrequency (RF) heating to a selected location within the human body to create thermal tissue necrosis.
In a normal heart, contraction and relaxation of the heart muscle (myocardium) takes place in an organized fashion as electrochemical signals pass sequentially through the myocardium from the sinoatrial (SA) node located in the right atrium to the atrioventricular (AV) node and then along a well defined route which includes the His-Purkinje system into the left and right ventricles. Sometimes abnormal rhythms occur in the atrium which are referred to as atrial arrhythmia. Three of the most common arrhythmia are: (1) ectopic atrial tachycardia, (2) atrial fibrillation, and (3) atrial flutter. Arrhythmia can result in significant patient discomfort and even death because of a number of associated problems, including: (1) an irregular heart rate, which causes a patient discomfort and anxiety; (2) loss of synchronous atrioventricular contractions which compromises cardiac hemodynamics resulting in varying levels of congestive heart failure; and (3) blood flow stasis, which increases the vulnerability to thromboembolism. It is sometimes difficult to isolate a specific pathological cause for the arrhythmia, although it is believed that the principal mechanism is one or a multitude of stray electrochemical circuits within the left and/or right atrium. These circuits or stray electrical signals are believed to interfere with the normal electrochemical signals passing from the SA node to the AV node and into the ventricles. Efforts to alleviate these problems in the past have included administering various drugs. In some circumstances, drug therapy is ineffective or wears off and frequently is plagued with side effects, such as dizziness, nausea, vision problems, and other difficulties.
An increasingly common medical procedure for the treatment of certain types of cardiac arrhythmia and atrial arrhythmia involves thermal ablation of heart tissue to cut off the path for stray or improper electrical signals. Such procedures may be performed by thermal ablation catheters. Typically, the ablation catheter is inserted in an artery or vein in the leg, neck, or arm of the patient and threaded, sometimes with the aid of a guidewire or introducer, through the vessels until a distal tip of the ablation catheter reaches the desired location for the thermal ablation procedure in the heart. RF ablation catheters produce thermal lesions and electrically isolate or render the targeted tissue non-contractile at particular points in the cardiac tissue by physical contact of the cardiac tissue with an RF electrode on the ablation catheter and application of RF energy through the RF electrode. The thermal lesion partially or completely blocks the stray electrical signals to lessen or eliminate arrhythmia.
Thermal ablation procedures, however, may be used to treat a variety of other conditions, not just atrial fibrillation. These conditions include liver and kidney disease, and cancer. Many more applications of thermal ablation procedures in the areas of reproductive health, the urinary tract, cosmetic surgeries, dermatology and neurology are currently being developed. Some of these, rather than employing a catheter, employ one or more minimally invasive RF needles or penetrating electrodes/antennas which is/are surgically inserted into the cancer tumor for example.
High-Intensity-Focused-Ultrasound (HIFU) is increasingly being used for performing lesion-making thermally ablative surgeries. With HIFU energy, physicians can create very precise, consistent, and effective thermally ablative lesions without stopping the patient's heart. In this already productized and available procedure, energy is applied to the outside of a beating heart epicardially. By adjusting acoustic power and wavelength, the acoustical energy is focused to ablate precise areas of cardiac tissue without impacting surrounding tissue or blood vessels, effectively creating continuous full-thickness lesions. An advantage of HIFU is that it is comparatively minimally invasive in that at-depth tissues can be lesioned from a nearby tissue or organ surface.
In HIFU, acoustic waves propagate through the tissue, and a portion of that wave energy determined by the tissue acoustic-attenuation is absorbed by the tissue and converted to heat. With the acoustic wave focused into beams, a very small acoustic focus may be achieved deep in tissue and the heat developed at that focus concentrated. If hot enough (65° to 85° C.), the tissue thermally coagulates in less than a second, wherein proteins denature and thermal ablation (tissue necrosis) occurs. At even lower temperatures of 45-65 degrees C., necrosis in tissue occurs in seconds, the hotter the faster. By focusing at more than one place or by scanning the focus, all of a target volume may be thermally ablated to a focal temperature.
Surgical ablation is often performed on patients already receiving cardiac valve replacement or repair, or coronary artery bypass, due to the fact that a surgeon already has access to the patient's heart and the above medical issue has caused AF to develop as a consequence. As HIFU surgical ablation enables less invasive procedures, increasing numbers of patients are becoming eligible for this as a standalone procedure.
A strategy wherein at least the acoustics-producing portions of an acoustic or HIFU surgical ablator device would be off-board the handheld ablator portion would allow for a disposable ablator applicator and a separately packaged acoustics-producing transducer in the console. This means that the applicator can be very inexpensive as it does not produce the acoustics; it just directs acoustics. Most existing acoustic ablators are handheld transducers which make their own acoustics with energy from an attached power cord. This makes them expensive-regardless of whether they can be reused or not.
Because most existing handheld ablators contain ultrasonic transducers, they are expensive to dispose of. If one reuses them, as is often the case, their lifetime and reliability will then be impacted by their repeated sterilization between patients.
What would be highly attractive is a disposable HIFU applicator which receives offboard acoustical energy from an attached console. Such an applicator would be connected to an acoustic energy waveguide, the purpose of which is to carry or transmit the acoustic energy from the console to the disposable applicator.
The information included in this background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded subject matter by which the scope of the invention is to be bound.